doc: Remove list of format fields

These are available in the output of -formats.

Similarily, we do not list the fields for e.g. -codecs.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Explain the various logevel settings

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Document which cpuflags exist

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Small grammar fix in -f description

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Fix grammar in -n description

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Grammar fixes for FFmpeg description

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Consistently use 'frame rate' everywhere

We used to use 'framerate' or 'frame rate' randomly.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Grammar fixes for FFmpeg's detailed description

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Consistently use 'filtergraph'

We used to use 'filtergraph' or 'filter graph' randomly.

'filtergraph' was chosen due to having 57 occurrences in
the documentation, whereas 'filter graph' had only 19.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Grammar fixes for stream selection

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Fix broken English in the common options description

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc: Grammar fixes for strem specifiers section

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>